For at least four decades, a thermoplastic-like material has been in use to mark stripes and symbols on roadways. A typical composition is (by weight): calcium carbonate 30-50%, reflective glass beads 30-50%, maleic-modified glycerol rosin ester 10-25%, rosin ester 1-9%, paraffinic wax 1-5%, and titanium dioxide 1-3%. See for example U.S. Pat. No. 3,679,626 to Tanekusa et al.
The most common practice currently is the supply of material in a pre-mixed, uncompounded powder/granular form, sealed in plastic bags weighing about 22 kg each. Typically, an operator loads the bags into an on-board melt kettle by hand. By heating to over 200° C. and stirring, the powder fuses and melts into a compounded liquid. The melted liquid requires continuous stirring to suspend the reflective glass beads prior to pumping and application to the roadway surface.
There are several problems associated with the current uncompounded powder:
1. The powder is dusty and has a tendency to settle out, causing the mixture to become non-uniform.
2. Shipping and handling leads to broken bags.
3. It is impractical to convey or ship the material in bulk non-bagged form.
4. The material has limited shelf life.
Alternatively, material has been delivered in pre-melted, compounded blocks that alleviate some of the problems encountered with powder. This method has been widely abandoned because the blocks require more time to melt than the powder/granular form. Also, the blocks have been found to interfere with the melt kettle stirring mechanism.
Improvements are desired for the supply of material, and for application of the material on roadways.